The present invention relates in general to an apparatus whose operation is controlled by a system such as a microcomputer including a processor or a microprocessor and a read-only memory (ROM), and more particularly this invention relates to an initial processing system, in the apparatus described above, at the time of automatic restoration of the processor or microprocessor after cutoff of a power source due to service failure, or the like, and to a processing system for data protection in the system described above at the time of cutoff of the power source.
A conventional service failure processing system is disclosed, for example, in Japanese Patent Publication No. 59-46001/1984. In accordance with this prior art reference, a processor determines whether a control operation is stopped or started again automatically in accordance with the drop of a power source voltage and the time period of the drop. If the service failure is an instantaneous service failure which does not render any particular problem, the control operation by the processor is automatically started once again. Automatic restoration of the processor is made in accordance with the condition of the instantaneous service failure in the construction described above.
If the power source voltage drops to a level which is somewhat insufficient for the operation of each circuit such as the microprocessor and yet permits its operation in the prior art publication described above, an abnormality interrupt signal is generated from a voltage monitor and is given to the control processor so that the operating condition of the control processor changes from "control" to "stop".
In the instantaneous service failure processing system described above, the service failure processing is carried out by selecting the processor operation either to halt or to completely stop in accordance with the drop of the power source voltage but a second processor (or register) is necessary for executing such a processing. Further, a power source of this register is necessary. Therefore, the control circuit gets complicated as a whole and becomes large in scale due to the space for the power source.
In the halt state of the processor operation, the power source is still supplied to the processor, the processor is still operable, input/output ports keep their outputs and each circuit is under the operating state. Accordingly, power consumption is not very large as a whole.
Though the prior art technique described above can bring the microprocessor to a halt by detecting the voltage, the microprocessor enters the stop state at the time of actual service failure or at the time of cutoff of the power source because no backup mechanism is provided. Therefore, the content of a random access memory (RAM) cannot be protected. Even if a backup mechanism is provided, it must have a capacity large enough to keep the operations of the input/output circuits and each circuit because they are still under the operating state and hence the mechanism becomes large in scale.
To solve such problems, the present invention provides a initial start processing system which can make an automatic return without requiring a register and a power source for the register.